One night as she lay down to sleep, a 60-year-old woman suddenly started having strange hallucinations. She told her doctors she heard music that seemed like it was playing from a radio at the back of her head.

Within a few months, she was hearing music all the time, with some songs on repeat for up to three weeks. Curiously, she did not recognize many of the tunes that dogged her, but they had full vocals and instrumentals; and when she sang or hummed the melodies for her husband, he identified them as popular songs.

"To our knowledge, this is the first report of musical hallucinations of non-recognizable songs that were recognized by others in the patient's environment," neurologists Danilo Vitorovic and José Biller of Loyola University Medical Center wrote. "This raises intriguing questions about musical memory, as well as mechanisms of forgetting."

Hallucinations occur when people have a sensory experience without any apparent stimuli — they see, hear, or even smell things that aren't there. Musical hallucinations are one form of auditory hallucinations, and they tend to occur in older people. Other conditions have been possibly linked to the experience, such as a hearing impairment, brain damage, epilepsy and psychiatric disorders, researchers say.

The woman described in the case report was hearing-impaired. She had previously been diagnosed with moderate hearing loss and tinnitus, a condition characterized by a ringing in the ears. She experienced some improvement in her hallucination symptoms when she was treated with carbamazepine, an anti-seizure drug, the researchers said.

Vitorovic and Biller write that her case begs for further study on what happens to forgotten memories. They propose that it's possible this patient had musical memories that were present, but not accessible.

"It is also possible that our patient had fragmented preservation of musical memories, with key portions of those memories lost, precluding recognition," the researchers wrote. "We find this proposition less likely since our patient would recognize music as familiar once it was played to her."